1. Field of the Invention
The present invention relates to a synchronous digital hierarchy system (SDH System), and more particularly to an add/drop cross connection apparatus for an SDH system.
2. Description of the Related Art
Cross-connects are electronic multiport switches for digital traffic and are known in the United States as digital cross-connect switches (DCSs) and as DXCs elsewhere. They are classified as DCS p/q or DXC p/q, where p is the hierarchical order of a port bit rate and q is the hierarchical order of the traffic component that is switched within that port bit rate.
DXC/DCS can occur in two main types. Higher order cross-connects, generally used to route bulk traffic in blocks of nominally 155 MBPS for network provisioning or restoration, and are designated as DXC 4/4. Lower order cross-connects (DXC 4/1, or 1/1) are used for time switching leased lines, consolidation, and service restoration.
In an add/drop cross connection apparatus of an exemplary SDH system, the data supplied from a west or east aggregate unit is divided into lower and the higher order path data. The lower order path data (or lower order virtual container (VC)) may be TU11 (Tributary Unit 11) or TU12 data processed by a TU pointer while the higher order path data (or higher order virtual container) may be AU3 (Administrative Unit 3) or AU4 data and has an AU pointer.
The lower order path data supplied from the west or east aggregate unit is matched to the system clock through a multiplex section adaptation circuit and supplied to a higher order path overhead monitor circuit. The higher order path overhead monitor circuits respectively monitors the higher order path overheads of the data respectively supplied from the multiplex section adaptation circuits, which are then delivered to the higher order path connection circuit. The higher order path connection circuit performs the cross connection to the lower order path data by space switching and supplying the lower order path data to the lower order path data processor, which performs the cross connection to the data, aligns the data, and detects and monitors various path overheads. The data processed by the lower order path data processor is delivered to a lower order tributary device.
Meanwhile, the higher order path data supplied from the west or east aggregate unit and supplied to the higher order path overhead monitor circuit is matched to the system clock through the multiplex section adaptation circuit. The higher order path overhead monitor circuit respectively monitors the higher order path overheads of the data respectively supplied from the multiplex section adaptation circuits and delivers the higher order path data to the higher order path connection circuit. The higher order path connection circuit performs the cross connection to the higher order path data by space switching and supplies the higher order path data to a higher order tributary device, which may be a known device such as DS3 (Digital Signal Level 3 of 44.736 MBPS), OC-1 (Optical Carrier supporting a Synchronous Transport Signal, Level 1 of 51.840 MBPS), STM-1 (Synchronous Transport Module, Level 1 of 155.520 MBPS) or STM-4 (Synchronous Transport Module, Level 4 of 622.080 MBPS) equipment. The SDH system is based upon the fundamental STM-1 rate, which is three times the fundamental SONET (Synchronous Optical NETwork) rate. The typical transmission media is defined to be an optical fiber, but the Broadband ISDN specification does define a User-Network Interface (UNI) STM-1 operating over coaxial cables.
In addition, the lower order path data supplied from the lower order tributary device is subjected through the lower order path data processor to the cross connection by time switching and delivered to the higher order path connection circuit. The higher order path connection circuit subjects the input data to cross connection by space switching and then supplies the data via a higher order unequipped generator to the west or east aggregate units. Meanwhile, the higher order path data supplied from the higher order tributary device is subjected through the higher order path connection circuit to cross connection by space switching and delivered through the higher order unequipped generator to the west or east aggregate units.
Hence, such add/drop cross connection apparatus is so complicated as to have one connecting path connecting it to the lower order tributary device and to separately have a second connecting path connecting it to the higher order tributary device.
Incorporated by reference herein are: U.S. Pat. No. 6,094,440 to Toshiki Sugawara et al. entitled Multiplex Type Transmitting Apparatus; U.S. Pat. No. 5,914,952 to Doo Seop Eom et al. entitled Tributary Unit Signal Cross-Connection Apparatus; U.S. Pat. No. 5,799,001 to Dong Choon Lee et al. entitled Composite Network Protective/Recovering Device For Synchronous Digital Hierarchy DXC; U.S. Pat. No. 5,777,998 to Giovanni Traverso et al. entitled Method And Circuit Arrangement For The Realization Of The Higher Path Adaptation/Mapping Function In Synchronous Digital Hierarchy/Optical Network Equipment; U.S. Pat. No. 5,574,717 to Masahito Tomizawa et al. entitled Line Terminating Equipment In SDH Networks, Using Forward Error Correcting Codes; and U.S. Pat. No. 5,555,248 to Eiji Sugawara entitled Tandem Connection Maintenance System.